High frequency switch

ABSTRACT

There is provided a high frequency switch which is satisfactory in terms of both insertion loss characteristics and harmonic characteristics. The high frequency switch includes: a common port outputting a transmission signal to an antenna; a plurality of transmission ports each having the transmission signal input thereto; and a plurality of switching units each connected between the plurality of transmission ports and the common port to conduct or block the transmission signal from each of the transmission ports to the common port, wherein each of the switching units includes a plurality of series-connected MOSFETs formed on a silicon substrate, the plurality of MOSFETs are any one of body contact-type FETs and floating body-type FETs, and each of the switching units includes both of the body contact-type FETs and the floating body-type FETs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/355,075, filed Jan. 20, 2012, the disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high frequency switch, and moreparticularly, to a high frequency switch used in a front end portion ofa wireless communications apparatus.

2. Description of the Related Art

Recently, a technology for implementing a high frequency switch used ina front end portion of a mobile phone, or the like, by a metal oxidesemiconductor field effect transistor (MOSFET) using a silicon oninsulator (SOI) process, has been developed.

Generally, a body (a well, a backgate) of the MOSFET using the SOIprocess is connected to ground potential (hereinafter, a field effecttransistor (FET), of which a body is connected to the ground potential,will be referred to a “body contact-type FET”) (please refer to JapanesePatent Laid-Open Publication No. 2005-515657).

However, when a high frequency switch is configured to use a bodycontact-type FET, good harmonic characteristics may be obtained therein;however, insertion loss characteristics are deteriorated, therebycausing difficulty in implementing the high performance of an apparatus.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a high frequency switchhaving good characteristics in terms of both of insertion losscharacteristics and harmonic characteristics through individualswitching units being configured to be collectively connected via acommon port using a combination of a body contact-type FET and afloating body-type FET (a FET of which a body reaches open circuitpotential) having good insertion loss characteristics.

According to an aspect of the present invention, there is provided ahigh frequency switch including: a common port outputting a transmissionsignal to an antenna; a plurality of transmission ports each having thetransmission signal input thereto; and a plurality of switching unitseach connected between the plurality of transmission ports and thecommon port to conduct or block the transmission signal from each of thetransmission ports to the common port, wherein each of the switchingunits includes a plurality of series-connected metal oxide semiconductorfield effect transistors (MOSFETs) formed on a silicon substrate, theplurality of MOSFETs are any one of body contact-type FETs and floatingbody-type FETs, and each of the switching units includes both of thebody contact-type FETs and the floating body-type FETs.

That is, the high frequency switch includes each switch unit connectedvia the common port and being configured using a combination of the bodycontact type FETs and the floating body type FETs having good insertionloss characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view showing a high frequency switch according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view showing a structure of a metal oxidesemiconductor field effect transistor (MOSFET) configuring a highfrequency switch according to an embodiment of the present invention;

FIG. 3 is a view showing a high frequency switch according to therelated art in which each MOSFET configuring a switching unit is formedof a body contact-type FET;

FIG. 4 is a view showing a high frequency switch in which each MOSFETconfiguring a switching unit is formed of a floating body-type FET; and

FIG. 5 is a view describing characteristics of a high frequency switchaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a high frequency switch according to an embodiment of thepresent invention will be described in detail.

FIG. 1 is a view showing a high frequency switch according to anembodiment of the present invention.

A high frequency switch is generally used in a front end portion of awireless communications apparatus and has a function of performing portswitching according to at least one of transmission and receptionswitching, a change of a transmission scheme, and switching of atransmission scheme.

FIG. 1 is a view showing a single pole double throw (SPDT) highfrequency switch according to the present embodiment. The high frequencyswitch according to the present embodiment may be a transmission-sidesingle pole double throw (SPDT) high frequency switch performing portswitching according to the switching of the transmission scheme. Thatis, the high frequency switch according to the present embodiment mayperform the switching (for example, switching between 850 MHz (a narrowband) and 1900 MHz (a wide band)) of a frequency band in a GSM terminal.

As shown in FIG. 1, the high frequency switch 1 may include first andsecond switching units 100A and 100B connected in common with (inparallel with) an antenna 110 through a common port CX.

The first switching unit 100A may be set to have a conductive state anda non-conductive state according to a control signal input to a firstcommon gate terminal GATE_TX1. The first switching unit 100A may conductor block a first transmission signal (for example, a transmission signalof 850 MHz) input to a first transmission port TX1 to the antenna 110through the common port CX.

The second switching unit 100B may be set to have a conductive state anda non-conductive state according to a control signal input to a secondcommon gate terminal GATE_TX2. The second switching unit 100B mayconduct or block a second transmission signal (for example, atransmission signal of 1900 MHz) input to a second transmission port TX2to the antenna 110 through the common port CX.

That is, any one of the first switching unit 100A and the secondswitching unit 100B is set to have a conductive state while the other isset to have a non-conductive state, whereby the high frequency switch 1may perform the switching of the transmission port. Hereinafter, aswitching unit in a conductive state refers to a switching unit of anon-port, and a switching unit in a non-conductive state refers to aswitching unit of an off-port.

The first switching unit 100A may include a plurality ofseries-connected MOSFETs T_(C11) to T_(C13) and T_(F11) to T_(F13). Thenumber of MOSFETs configuring the first switching unit 100A may beappropriately changed by withstand voltage required in the highfrequency switch 1. Here, each of the MOSFETs T_(C11) to T_(C13) andT_(F11) to T_(F13) has a source terminal and a drain terminal,indistinguishable from each other on a structure of the MOSFET.Therefore, in the present specification, the “series-connected” MOSFETsmean that any one of a source terminal and a drain terminal of oneMOSFET is connected to any one of a source terminal and a drain terminalof another MOSFET. In addition, each of the MOSFETs T_(C11) to T_(C13)and T_(F11) to T_(F13) will be described as an n-type MOSFET.

FIG. 2 is a cross-sectional view showing a structure of a MOSFETconfiguring the high frequency switch according to the embodiment of thepresent invention.

As shown in FIG. 2, the MOSFETs T_(C11) to T_(C13) and T_(F11) toT_(F13) may be formed on a silicon on insulator (SOI) substrate . TheMOSFETs T_(C11) to T_(C13) and T_(F11) to T_(F13) formed on the SOIsubstrate 200 may have a structure in which MOSFET devices formed on asilicon layer 220 disposed on an insulation layer 210 formed of asilicon oxide (SiO₂) are enclosed by the insulation layer 210 and may beelectrically separated from each other by the insulation layer 210.

The MOSFETs T_(C11) to T_(C13), among the MOSFETs T_(C11) to T_(C13) andT_(F11) to T_(F13) configuring the first switching unit 100A, connectedto the common port CX in positions adjacent thereto, may have bodiesgrounded through body resistors R_(b11) to R_(b13). That is, the MOSFETsT_(C11) to T_(C13) may be a body contact-type FET. The body resistorsT_(b11) to R_(b13) are provided in order to reduce loss due to powerleaked from a body region.

Meanwhile, voltage is not applied to bodies of the MOSFETs T_(F11) toT_(F13), among the MOSFETs T_(C11) to T_(C13) and T_(F11) to T_(F13)configuring the first switching unit 100A, connected to the common portCX in positions distant therefrom, such that the bodies of the MOSFETsT_(F11) to T_(F13) reaches an open circuit potential. That is, theMOSFETs T_(F11) to T_(F13) may be a floating body-type FET.

In addition, gate resistors R_(g11) to R_(g16) may be individuallyprovided between gate terminals of the MOSFETs T_(C11) to T_(C13) andT_(F11) to T_(F13) and the first common gate terminal GATE_TX1.

The second switching unit 100B also has the same structure as that ofthe first switching unit 100A. Therefore, a description thereof will bebriefly described or be omitted.

The second switching unit 100B may include a plurality ofseries-connected MOSFETs T_(C21) to T_(C23) and T_(F21) to T_(F23) andeach of the MOSFETs T_(C21) to T_(C23) and T_(F21) to T_(F23) may beformed on the SOI substrate 200.

The MOSFETs T_(C21) to T_(C23), among the MOSFETs T_(C21) to T_(C23) andT_(F21) to T_(F23) configuring the second switching unit 100B, connectedto the common port CX in positions adjacent thereto, may be a bodycontact-type FET and have bodies grounded through body resistors R_(b21)to R_(b23). Meanwhile, the MOSFETs T_(F21) to T_(F23), connected to thecommon port CX in positions distant therefrom, may be a floatingbody-type FET.

In addition, gate resistors R_(g21) to R_(g26) may be individuallyprovided between gate terminals of the MOSFETs T_(C21) to T_(C23) andT_(F21) to T_(F23) and the second common gate terminal GATE_TX2.

An operation of the high frequency switch 1 according to the presentembodiment will be described.

A case in which the first switching unit 100A is an on-port and thesecond switching unit 100B is an off-port will be described. Inaddition, a case in which the first switching unit 100A is an off-portand the second switching unit 100B is an on-port may also be considered(a description of this case will be omitted).

When a high level control signal is input to the first common gateterminal GATE_TX1, all of the MOSFETs T_(C11) to T_(C13) and T_(F11) toT_(F13) of the first switching unit 100A are conductive. Therefore, thefirst switching unit 100A is switched on, such that the firsttransmission signal input to the first transmission port TX1 istransferred to the antenna 110 through the common port CX.

At this time, since a low level control signal is input to the secondcommon gate terminal GATE_TX2, all of the MOSFETs T_(C21) to T_(C23) andT_(F21) to T_(F23) of the second switching unit 100B are switched to anon-conductive state. Therefore, since the second switching unit 100B isswitched off, even in the case in which a signal is input to the secondtransmission port, the signal is not transferred to the antenna 110through the common port CX.

The high frequency switch 1 according to the present embodiment mayperform the switching of the transmission port by the above-mentionedoperation.

FIG. 3 is a view showing a high frequency switch according to therelated art in which each MOSFET configuring a switching unit is formedof a body contact-type FET.

In the case of the high frequency switch according to the related artshown in FIG. 3, with regard to transmission characteristics, harmoniccharacteristics from the first transmission port TX1 to the common portCX are satisfactory; however, insertion loss characteristics aredeteriorated. Since the insertion loss characteristics may directlyaffect power amplifier efficiency, additional improvements are required.However, it is relatively difficult to satisfy specifications requiredin order to implement high performance in an apparatus with the relatedart high frequency switch shown in FIG. 3.

FIG. 4 is a view showing a high frequency switch in a case in which eachMOSFET configuring a switching unit is formed of a floating body-typeFET.

The high frequency switch shown in FIG. 4 includes a floating body-typeFET having relatively good loss characteristics in a device unit.Therefore, insertion loss characteristics from the first transmissionport TX1 to the common port CX are satisfactory. However, in the highfrequency switch including the floating body-type FET, harmoniccharacteristics are deteriorated.

That is, a first transmission signal V_(TX1) output to the common portCX through the first switching unit 100A is also applied to the secondswitching unit 100B connected, together with the first switching unit100A, to the common port CX. In this case, the first transmission signalV_(TX1) output to the common port CX through the first switching unit100A of an on-port, is affected by characteristics (characteristics atthe time of the transistor off state) of MOSFETs T_(F21) to T_(F26)configuring the second switching unit 100B of an off-port. In addition,in the case in which the second switching unit is formed of a floatingbody-type FET, since an influence of the second switching unit of theoff-port on harmonic characteristics of the first transmission signaloutput to the common port becomes relatively large, harmoniccharacteristics of the high frequency switch 1 are deteriorated.

In addition, when the first switching unit 100A is switched off, thesecond switching unit 100B is switched on, such that both of theswitching units generally required to have the same configuration.

FIG. 5 is a view describing characteristics of a high frequency switchaccording to an embodiment of the present invention.

As shown in FIG. 5, the high frequency switch 1 according to the presentembodiment may include the first and second switching units 100A and100B, in which the MOSFETs T_(C11) to T_(C13) and T_(C21) to T_(C23),among the MOSFETs configuring the respective switching units 100A and100B, connected to the common port CX in positions adjacent thereto, maybe formed of a body contact-type FET, and the remaining MOSFETs T_(F11)to T_(F13) and T_(F21) to T_(F23) may be formed of a floating body-typeFET.

Since parasitic capacitance components and parasitic resistancecomponents are present in the plurality of MOSFETs configuring eachswitching unit 100A and 100B, voltage applied to each MOSFET may not beevenly divided. That is, voltage applied to the MOSFETs T_(C11) toT_(C13) and T_(C21) to T_(C23), among the series-connected MOSFETs ofeach switching unit 100A and 100B, connected to the common port CX inpositions adjacent thereto, becomes relatively large.

Therefore, an influence of the MOSFETs T_(C21) to T_(C23) and T_(F21) toT_(F23) configuring the second switching unit 100B, which is theoff-port side, on harmonic characteristics of the first transmissionsignal V_(TX1) output to the common port CX becomes relatively large inthe MOSFETs adjacent to the common port CX.

Therefore, each switching unit 100A and 100B has the body contact-typeFETs connected to the common port CX in the positions adjacent thereto,whereby deterioration in the insertion loss characteristics of the highfrequency switch 1 may be effectively prevented. Further, in eachswitching unit 100A and 100B, FETs other than the body contact-type FETsare formed of the floating body-type FETs, whereby the insertion losscharacteristics of the high frequency switch 1 may be improved.

The high frequency switch according to the embodiment of the presentinvention has the following effects. That is, each switching unitconnected via the common port is configured using a combination of thebody contact-type FETs and the floating body-type FETs having goodinsertion loss characteristics, whereby a high frequency switch havinggood characteristics in terms of both insertion loss characteristics andharmonic characteristics may be realized.

The present invention is not limited to the high frequency switchaccording to the above-described embodiments. That is, a high frequencyswitch according to an embodiment of the present invention may be atransmission and reception single pole 4 throw (SP4T) high frequencyswitch performing port switching according to the switching of thetransmission and reception scheme. In addition, a high frequency switchaccording to an embodiment of the present invention may also be a singlepole multi throw (SPMT) switch and a multi pole multi throw (MPMT).

In addition, any one of the MOSFETs configuring each switching unit maybe formed of the floating body-type FET, and a ratio of the bodycontact-type FETs to the floating body-type FETs and a connectionposition therebetween are not limited.

Further, the MOSFETs of each switching unit are not limited to then-type MOSFET, but may also be a p-type MOSFET .

In addition, the MOSFET is not limited to being formed on the SOIsubstrate, but may also be formed on a general silicon substrate.

As set forth above, according to embodiments of the present invention, ahigh frequency switch which is satisfactory in terms of both harmoniccharacteristics and insertion loss characteristics may be realized.

While the present invention has been shown and described in connectionwith the embodiments, it will be apparent to those skilled in the artthat modifications and variations can be made without departing from thespirit and scope of the invention as defined by the appended claims.

What is claimed is:
 1. A high frequency switch comprising: a common portreceiving and transmitting a high frequency signal through an antenna; afirst switching unit including at least one a first floating body-typeswitch and at least one first body contact-type switch connected inseries and allowing the high frequency signal to be conducted orpreventing the high frequency signal from being conducted to a signalpath between a first port receiving and transmitting the high frequencysignal and the common port; and a second switching unit including atleast one second floating body-type switch and at least one second bodycontact-type switch connected in series and allowing the high frequencysignal to be conducted or preventing the high frequency signal frombeing conducted to a signal path between a second port receiving andtransmitting the high frequency signal and the common port.
 2. The highfrequency switch of claim 1, wherein the first body contact-type switchis connected to the common port in a position closer than that of thefirst floating body-type switch, and the second body contact-type switchis connected to the common port in a position closer than that of thesecond floating body-type switch.
 3. The high frequency switch of claim1, wherein the first and second body contact-type switches and the firstand second floating body-type switches are field effect transistors(FETs).
 4. The high frequency switch of claim 1, wherein a body terminalof the first body contact-type switch is grounded through a first bodyresistor, and a body terminal of the second body contact-type switch isgrounded through a second body resistor.
 5. The high frequency switch ofclaim 1, wherein the first and second body contact-type switches and thefirst and second floating body-type switches are formed on a siliconsubstrate.
 6. The high frequency switch of claim 5, wherein the siliconsubstrate is a silicon-on-insulator (SOI) substrate.